This invention relates generally to radio frequency signal direction finding apparatus and more particularly to types of such apparatus which measure the phase differences between received radio frequency signals having frequencies over a wide band of frequencies and having relatively short time durations.
As is known in the art, interferometer antenna signals have been used to provide accurate direction finding wherein a pair of antennas, spatially displaced a predetermined distance, receive signals with phase differences related to the predetermined distance of separation, the frequency of the received signals and the angular direction of the source of such received signals. Such systems have been suggested in U.S. Pat. No. 3,221,251 and U.S. Pat. No. 3,611,135. In order to provide amplification to the received radio frequency signals a pair of traveling wave tube (TWT) amplifiers is coupled to the pair of antennas. With such arrangement it is necessary that the phase shifts provided by the TWT amplifiers be proprely balanced or matched over a wide range of operating frequencies and signal strengths in order to obtain a proper measure of the phase shift between the received signals and hence a proper determination of the angular direction of the source of the radio frequency signal.
In a known system one of the pair of antennas is fed to a phase modulation section made up of plurality of switched delay lines. The output of the phase modulation section is a phase modulated signal which, when combined with the signal received at the other one of the pair of antennas, provides a composite, amplitude modulated signal. The composite amplitude modulated signal is then amplified in a radio frequency amplifier. The amplified signal is then compared with the phase modulating signal fed to the phase modulation section which is used to switch the delay lines to provide an output signal indicating the phase difference between the signals received by the pair of antennas and hence an indication of the direction of the received signals. While such technique may be useful in many applications, such technique has a relatively narrow operating bandwidth.